sub system

So, I am a substitute teacher and get called to sub all the time, which is great. However, I can only be at one place at a time. A few of the sub systems for the larger districts are called by computer and the private schools have a person calling you. I was called by a local private school earlier and I told them I am already working elsewhere but to please call me next time. Since tomorrow I am already subbing at a local school and so far have been called by RISD three times to sub for tomorrow. If you can not sub they have a menu for you to select the reason why, such as working in other district, sick, etc. So, today when it called me at 4:28 PM I went through the choices and pressed the number for already working in another district. TWO minutes later at 4:30, after I pressed that the computer system called AGAIN! So, I went through the system and did the same thing. After that I went online, and told it not to call me from today at 4:40- to tomorrow at the same time. At 5:00 PM it calls AGAIN! So, I pressed star for it not to call me during this calling period, which I had already done online. This is the first time I have done that and had the computer system still call me. So, my question is why do they even have a menu if obviously, it does not matter what you push it will still call you! Frustrated, just a bit over this. Please let me know your thoughts.